An appendage (or outgrowth) is an external body part, or natural prolongation, that protrudes from an organism's body. In arthropods, an appendage refers to any of the

homologous Homology may refer to: Sciences Biology *Homology (biology), any characteristic of biological organisms that is derived from a common ancestor *Sequence homology, biological homology between DNA, RNA, or protein sequences * Homologous chrom ...

body parts that may extend from a body segment, including antennae,

mouthparts Mouthparts may refer to: * The parts of a mouth ** Arthropod mouthparts *** Insect mouthparts {{disambig ...

(including mandibles, maxillae and maxillipeds), gills, locomotor legs (

pereiopod The decapod (crustaceans such as a crab, lobster, shrimp or prawn) is made up of 20 body segments grouped into two main body parts: the cephalothorax and the pleon (abdomen). Each segment may possess one pair of appendages, although in various g ...

s for walking, and

pleopod The decapod ( crustaceans such as a crab, lobster, shrimp or prawn) is made up of 20 body segments grouped into two main body parts: the cephalothorax and the pleon (abdomen). Each segment may possess one pair of appendages, although in various ...

s for swimming), sexual organs ( gonopods), and parts of the tail ( uropods). Typically, each body segment carries one pair of appendages. An appendage which is modified to assist in feeding is known as a maxilliped or gnathopod. In vertebrates, an appendage can refer to a locomotor part such as a tail, fins on a fish,

limb Limb may refer to: Science and technology * Limb (anatomy), an appendage of a human or animal *Limb, a large or main branch of a tree *Limb, in astronomy, the curved edge of the apparent disk of a celestial body, e.g. lunar limb *Limb, in botany, ...

s ( legs, flippers or wings) on a tetrapod; exposed sex organ; defensive parts such as horns and

antler Antlers are extensions of an animal's skull found in members of the Cervidae (deer) family. Antlers are a single structure composed of bone, cartilage, fibrous tissue, skin, nerves, and blood vessels. They are generally found only on male ...

s; or

sensory organ A sense is a biological system used by an organism for sensation, the process of gathering information about the world through the detection of stimuli. (For example, in the human body, the brain which is part of the central nervous system rec ...

s such as auricles, proboscis (

trunk Trunk may refer to: Biology * Trunk (anatomy), synonym for torso * Trunk (botany), a tree's central superstructure * Trunk of corpus callosum, in neuroanatomy * Elephant trunk, the proboscis of an elephant Computing * Trunk (software), in rev ...

and

snout A snout is the protruding portion of an animal's face, consisting of its nose, mouth, and jaw. In many animals, the structure is called a muzzle, rostrum, or proboscis. The wet furless surface around the nostrils of the nose of many mammals is c ...

) and barbels. Appendages may become ''uniramous'', as in insects and

centipede Centipedes (from New Latin , "hundred", and Latin , " foot") are predatory arthropods belonging to the class Chilopoda (Ancient Greek , ''kheilos'', lip, and New Latin suffix , "foot", describing the forcipules) of the subphylum Myriapoda, an ...

s, where each appendage comprises a single series of segments, or it may be ''biramous'', as in many crustaceans, where each appendage branches into two sections. ''Triramous'' (branching into three) appendages are also possible. All arthropod appendages are variations of the same basic structure (''homologous''), and which structure is produced is controlled by "

homeobox A homeobox is a DNA sequence, around 180 base pairs long, that regulates large-scale anatomical features in the early stages of embryonic development. For instance, mutations in a homeobox may change large-scale anatomical features of the full- ...

" genes. Changes to these genes have allowed scientists to produce animals (chiefly '' Drosophila melanogaster'') with modified appendages, such as legs instead of antennae.

References

See also